Tamping machine



July 28, 1953 A. GODENIR 46,7

I TAMPING MACHINE Filed Feb. 17, 1949 5 Sheets-Sheet 1 July 28, 1953 A. GODENIR TAMPING MACHINE Filed Feb. 1'7, 1949 3 SheetsSneet 3 ALBERT 'aDEN/E 3/. I MM, fix:

Patented July 28, 1953 direct and mesne assignments, to The Cementation Company Limited, London, England, a

British company Application February 17, 1949, Serial No. 76,977 In Great Britain November 11, 1946 Claims. 1

)This invention relates to tamping apparatus for treating surfaces in the construction of roads, aircraft landing strips and the like.

It has been found difficult to tamp a surface satisfactorily without the employment of manual labour, and it is an aim of the present invention to devise a power driven tamping unit which will allow rapid and satisfactory tamping to be carried out.

:In accordance with the invention there is provided a tamping unit, comprising a tamping hammer, an eccentric device for producing an oscillating motion, spring means arranged to connect the hammer and the eccentric device, a tamping shoe plate positioned to receive impacts from the hammer and to transmit the same to the surface being tamped, and power driving mean for the eccentric device, the speed of the drive to the eccentric device, the effective mass of the tamping hammer and the spring means being chosen to ensurethat thehammer has a relatively high velocity at the time of impact. The invention lends itself readily to the provision of a composite tamping machine comprising several of the units just defined connected side by side, and further comprising means; for supporting the assembled units to allow themto be displaced over a surface to be tampe'd in a direction substantially transverse to the line of connection of the said units.

For a better understanding oftheinature of the invention and to show how the same may be carried into effect reference will now be made to the accompanying drawings in which:

Figure 1 is a front elevation showing a constructional example of a tamping unit made in accordance with the invention,

Figure 2 is a side elevation corresponding to Figure 1, and,

Figure 3 indicates diagrammatically how several of the units shown in Figures-1 and 2 may be connected. to produce a composite tamping machine. ---Referring first to Figures 1 and 2, the tamping unit essentially comprises a framework having vertical membersieand top and bottom plate members 2 and 3 respectively. The upper plate member 2 is held in rigid spaced relation with the lower plate member 3 by the employment of rods 4 'The latter serve to support a platform 5 upon which there is mounted a suitable power unit 6. In this example the power unit consists of a two--, stroke internal combustion engine. The power output shaft of the. internal combustion engine 6 isjindicated at I, and it will be noted that a double pulley 8 is'mounted thereon.

The upper plate member 2 has hanger bearings 9 depending therefrom, such hanger bearings serving to support a shaft E0. The shaft has a pulley ll keyed thereto, such pulley being driven by a belt I2 which receives power from one pulley groove of the double pulley B. An eccentric collar i3 is fixed upon the shaft II), the collar having a ball race l4 thereon. The outer annulus of the ball race is enclosed in a cage comprising an upper plate l5 and a lower plate I6 connected by four heavy bars ll. The outer annulus of the ball race l4 slidably contacts the upper and lower plates l5 and iii to raise and lower the cage. The bars I! are of circular section, and as seen in Figure 2, they lie closely on either side of the shaft Ill. The bars I! thus ensure that the cage is restricted in its movements to vertical reciprocation relative to the shaft [0 under the action of the eccentric collar l3.

A coil spring 20 is attached at one end to the lower plate [6 of the cage, the other end of such spring being attached to the upper end of a hammer 2|. The lower end of the hammer has a reduced diameter face portion 22 which enters an aperture 23 formed in the plate member 3. The face member 22 is adapted to encounter a boss 24 formed integrally upon one side of a shoe plate 25. The latter is pivotally supported as at 26, and curves upwardly towards the front end on which is attached an angle bracket 21. A spring 28 extends from the angle bracket to a convenient point of anchorage on the framework.

In the employment of the unit described above, the engine 6 is set in motion, and thence power istransmitted from the shaft I to the shaft Ii Rotation of the shaft [5 causes the cage including the plate It to be reciprocated vertically with harmonic motion. The movements of the cage are transmitted through the spring 20 to the hammer 2|. The latter strikes the boss 24 and hence causes the shoe 25 to transmit a tamping action to the ground onwhich the tamping unit is located.

In, assembling several of the tamping units to form a composite tamping machine, they may be coupled in the manner indicated in Figure 3. It will be observed from Figure 3 that four tamping units are coupled side by side. According to requirements, any desired number of tamping units may be coupled in the same fashion. The coupled units may all be carried on wheels W running on rails B. To understand how the coupling as between the adjacent units is effected, it will sufiice to indicate how the units and 5! are relatively arranged. The unit 5| has its double pulley 8A driving through a belt [2A to the pulley HA. The double pulley SA has a second belt I2B thereon which co-operates with a pulley HB associated with the adjacent unit 55. As appears best in the illustration of the unit shown in Figure 1, with which the unit 55 may be identified, the pulley MB is disposed upon the shaft l5, being fixed thereon, and hence the engine 6A of the tamping unit 51 serves apparently to drive 4 of contact with the shoe, the available kinetic energy would be negligible or extremely low. In order to ensure that the hammer 2| is travelling downwardly at its maximum velocity at the instant it contacts the tamping shoe plate 25, the spring 20 of a device embodying the present invention has a stiifness which is substantially equal to the product of the mass of the hammer not only its own tamping unit 5i but also the tamping unit 55. In fact the tamping unit 50 has its own engine 5, and therefore the double pulley arrangement serves merely to ensure synchronism between the engines 6 and 6A. As is well known, small two-stroke internal combustion engines can be adjusted to run at fixed speeds within certain limits. be exactly adjusted by simple methods, and since in any case the engines may not necessarily maintain their adjusted speeds, it is important to ensure that the engines are interconnected in the manner indicated, to obtain synchronism in their operation. The connections afforded by the double-belt systems allow the connecting units to be relatively adjusted so that the individual eccentric devices thereof operate out of mechanical phase. If there are four units connected as shown, then an adjustment is made to ensure that the eccentric devices operate 45 out of phase progressively as between one unit and the next. Thus between the two end units there is a phase displacement of a half cycle 1. e. 180.

It is highly desirable to ensure that the phase displacement as between the individual units of a machine does in fact occur, since if all the hammers of the units struck at the same time, the piece of road surface or the like that is being tamped would be reduced in height along a lateral or transverse strip, so that in order to move the machine progressively to carry out further tamping, it would then be necessary virtually to lift the machine to the height of the untamped material. By ensuring that the tamping takes place progressively transversely with reference to the line of advancement of the machine, it is possible to move the machine easily forward. Thus a handle H may be provided, such handle being connected through sprocket wheels and chains to the axle A of the wheels W. An operator can manually cause the machine to travel forward on the rails R. handle H.

The angle brackets 2'! of the individual units serve to ensure that a ridge of uncompacted material to be tamped will not build up in front of the machine to an extent where the material will pour over the tamping shoes 25 and clog the mechanism. When it is desired to clean the individual units, it is simply necessary to release the springs 28 to allow the shoes 25 to be drawn downwardly, whereupon loose material can be removed from within the shoes.

The choice of the spring 25) of each unit in relation to the speed at which the engine thereof runs and the effective mass of the hammer 2|, represents an important feature of this present invention. It will be obvious that if the hammer 2! were connected to the eccentric device by a rigid link, the hammer 2! would move with simple harmonic motion, with the result that the hammer would have zero velocity when at the lowest position in its path of movement. Since the tamping action of the hammer 2| through the shoe 25 will depend upon the available kinetic energy, if the hammer is moving at zero velocity or at a velocity approaching zero at the instant by simply turning the Since these speeds cannot 2E and the square of the angular velocity of the eccentric l3 so that the maximum velocity of the hammer 21 occurs when the eccentric I3 is in its bottom-dead-center position, and the spring 28, attached to the tamping shoe plate 25, yieldably holds the latter in a position to be contacted by the hammer 2| when the eccentric I3 is in said bottom-dead-center position.

In order to prove that the maximum velocity of the hammer 2| will occur at the bottom-deadcenter position of the eccentric l3 only when the stiffness of the spring 20 is substantially equal to the product of the mass of the hammer and the square of the angular velocity of the eccentric:

Let:

M :mass of the hammer a=radius of eccentricity of the eccentric y=vertical component of the displacement of the eccentric w=rotationa1 speed of the eccentric in radians per unit time p==spring stiffness t=time from the beginning of a cycle which commences with the eccentric at bottom dead cen-'- ter ac vertical displacement of the hammer zt velocity of the hammer $=acceleration of the hammer.

By geometry, y=aa cos mi The deflection of the spring=ya: and, by substitution,

y-.1:=aa cos wt-:v (1) From Newton's Law (Force==Mass acceleration) the following is obtained:

Since w, p and M are all real constants, it is justifiable to let Substituting (4) in (3), Equation 3 becomes:

i+w a x=w a a(lcos wt) (5) Equation 5 can be solved with the elimination of arbitrary constants on the basis that, t=0, 00:0 and i=0 to give a solution:

From Equation 6, by difierentiating, a: and it can be found. It is required that will be maximum when 23:0 and when wt=21r (that is, when the eccentric is at its bottom-dead-center position). Examination of c and :c' with 21 substitut ed for mi shows that the above requirements are satisfied only when =1.

x=a- (04 cos wt-cos amt) When (1:1, a =1 and Equation 4 becomes simply i and Equation 5 can now be rewritten as:

Equation '7 can be solved with elimination of arbitrary constants, as before, to give the following solution From Equation 9 it can be seen that a: is a maximum when wt=21r, and from Equation 10 it will be noted that, with wt=21r, a:=zero.

Therefore, the required conditions are satisfied, that is, the hammer velocity is a maximum and the hammer acceleration is zero with the eccentric at bottom dead center, only when Knowing the mass of the hammer and the angular velocity of the eccentric, the required spring stiifness can be easily determined, and the dimensions and material of the spring are then selected to provide this required spring stiffness.

Further, the spring 28 attached to the framework and to the bracket 21 at the front end of the pivoted tamping shoe plate 25 operates to yieldably hold the latter in a position against the lower plate member 3 in which the boss 24 is struck by the hammer 2| at the instant when the latter is travelling downwardly at its maximum velocity. Since the maximum velocity of the hammer occurs when the acceleration of the hammer is zero and the eccentric is at bottom dead center, it is apparent that the spring 20 must then have its normal or substantially unfiexed length (that is, the spring length when it is stressed only by the weight of the hammer suspended therefrom). Thus, the distance between the surface of the boss 24 and the axis of rotation of the shaft Ill, with the tampin shoe plate held against the lower plate member 3, must be substantially equal to the sum of the maximum radius of the eccentric collar 13, the thicknesses of the races of the ball bearing on the eccentric collar and of the plate IS, the normal length of the spring 20 and the total length of the hammer 2|.

While I have described and shown illustrative embodiments of the invention, it is to be understood that the present invention is not limited to these precise embodiments and that various changes and modifications may be effected therein without departing from the scope or spirit of the present invention as defined in the appended claims.

What is claimed is:

1. A tamping unit comprising a tamping hammer, spring means connected at one end to said tamping hammer for the suspension thereof, an eccentric device for producing harmonic oscillating motion in the vertical direction, frame means supporting said eccentric device, means operatively connecting the other end of said spring means to said eccentric device to transmit the oscillating harmonic motion to said spring means, a source of power for rotating said eccentric device at a substantially uniform pre-determined angular speed, the spring stiffness of the spring means being substantially equal to the product of the mass of the ham-F mer and the square of the said substantially uniform pre-determined'angular velocity so that said hammer travels downwardly at its 'maximum velocity when said eccentric device is' disposed with its maximum eccentricity in the downward direction, a tamping shoe plate separate from said hammer and movably mounted on said frame means below said hammer and in the path of movement of the latter, and means yieldably'holding said tamping shoe plate in a position which is located a distance from the axis of said eccentric device equal to the distance from the bottom of said hammer to said axis when the eccentric device is disposed with its maximum eccentricity in the downward direction and said spring means is stressed only by the weight of said hammer suspended therefrom, so that said tamping shoe plate is contacted by said hammer at substantially the instant when the latter is travelling downwardly at said maximum velocity thereof.

2. A tamping unit comprising a tamping hammer, an eccentric device for producing harmonic oscillating motion in the vertical direction, spring means of pre-determined stillness, means for operatively connecting one end of said spring means to said eccentric device, means connecting the other end of said spring means to the hammer for the suspension of the hammer upon said spring means, a, frame rotatably supporting said eccentric device, a source of mechanical power for rotating said eccentric device at a substantially uniform pre-determined angular velocity, the spring stiffness of the spring means being substantially equal to the product of the mass of the hammer and the square of said angular velocity so that said hammer travels downwardly at its maximum velocity when said eccentric device is disposed with its maximum eccentricity in the downward direction, a tamping shoe plate separate from said hammer, means movably mounting said shoe plate on said frame below said hammer and in the path of movement of the latter, and resilient means yieldably holding said tamping shoe plate in a position located a distance from the axis of rotation of said eccentric device equal to the sum of the maximum eccentricity of said eccentric device, the length of the connecting means between said spring means and said eccentric device, the normal length of said spring means when the latter is stressed only by the weight of said hammer suspended therefrom and the length of said hammer, so that the tamping shoe plate is contacted by the tamping hammer at substantially the instant when the latter is travelling downwardly at said maximum velocity thereof.

3. A tamping machine comprising several of the units according to claim 1, an elongated frame for the mounting of the units side by side, and running wheels for the support of the frame to permit the latter to be displaced in a direction substantially transverse to its length.

4. A tamping mechane comprising several of the units according to claim 1, an elongated 7 frame for the support of said units side by side, a mechanical connection efiectively between the several eccentric devices to ensure that they rotate with a common angular velocity wherebythe eccentric devices of the units may be driven in synchronism with a pre-determined phase difl'erence.

5. A 'tamping unit comprising a tamping hammer, an eccentric device for producing harmonic oscillating motion, a source of mechanical power for rotating said eccentric device with a substantially uniform pre-determined angular veiocity, spring means having a spring stiifness substantially equal to the product of the mass of said hammer and the square of said angular velocity, means connecting one end of said spring means to said eccentric device, means connecting the other end of said spring means to said hammer for suspending the latter from said spring means, and a displaceable shoe-plate dis- 8 posed beneath the hammer and separate from the latter to receive the tamping impact thereof and transfer the same to the surface to be tamped, said shoe-plate being pivotally supported to permit withdrawal thereof away from said hammer for cleaning.

ALBERT GODENIR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,070,326 Coutant et a1. Aug. 12, 1913 1,887,341 Venable Nov. 8, 1932 1,926,193 Clark Sept. 12, 1933 1,943,076 Jackson Jan. 4, 1934 1,953,825 Finley et a1. -1.. Apr. 3, 1934 2,098,895 Velten Nov. 9, 1937 2,160,462 Schieferstein May 30, 1939 

